BACKGROUND OF THE INVENTION
The present invention relates to a machine that handles vials containing chemical specimens or samples and moves vials from storage trays to one or more sample stations on the machine under software control.
Gas chromatographs and similar chemical species analyzers such as mass spectrometers are known. Vial handling machines, such as the model 7000 Headspace Autosampler sold by Tekmar Co., Cincinnati, Ohio, USA, are also known. The model 7000 extracts from a covered vial a predetermined amount of fluid from a static gaseous headspace above a sample, and conveys the predetermined amount of fluid (containing volatiles to be identified) to a gas chromatograph. Vial autosamplers using dynamic headspace techniques are also known, such as the model PTA-30W/S Autosampler sold by Dynatech Precision Sampling Corp., Baton Rouge, La., USA. The model PTA-30W/S routes a purge gas into a covered vial containing a sample, and provides an outlet from the vial to carry the exiting fluid (comprising the purge gas and volatile components from the sample) to a separate concentrator trap unit.
In one aspect of the present invention, a vial handling device comprises a base unit and a sampling module adapted to mate with the base unit. The vial handling device has a vial storage area on the base unit to hold multiple vials in known locations, and a sampling station in the sampling module where fluid is removed from the vial. The vial transporter has a controlled arm with a vial gripper for moving a vial between the storage area and the sampling station. The sampling module has a needle assembly to penetrate the vial to remove the fluid, and mates with the base unit proximate the sampling station. In a preferred embodiment, the base unit has two sampling stations.
The vial transporter arm projects from the base unit along a first (Y) axis, and the main arm is adapted for translation along a second (X) axis substantially perpendicular to the first axis. The vial transporter also includes a vial gripper head assembly adapted for movement along the main arm in the Y axis. The vial gripper assembly includes a gripper head adapted for translation along a third (Z) axis substantially perpendicular to the first and second axes. The position of the gripper assembly and gripper head in the X and Y directions are sensed by potentiometers which are used to provide position information. The indicated position of the gripper assembly is calibrated relative to a known reference such as a fixed home position each time the autosampler is started, or at operator selected times, to insure accurate positioning of the vial transporter. The travel of the gripper assembly is sensed with suitable sensors, as disclosed beam interrupters that will provide position information relating to a known mechanical calibration position on the base unit. The gripper assembly scale along its X and Y axes between sensed limits is calibrated by determining a digital count from the analog voltage from the position indicating potentiometers and correlating that count to the known distance between limits. Software adjustments are made as required to the scale (counts per inch) for the X and Y axes so that the positioning system for the vial transporter stays in calibration.
Additionally, the vial storage area utilizes trays or racks that have receptacles for the vials to be stored and moved to various stations for the vials and ultimately to the sampling modules. A calibration system is utilized in connection with the gripper assembly with position sensors for determining the orthogonality of the storage trays or racks, using a mechanical sensing bar positioned in each of the racks (two racks are used preferably) and by determining the actual Y axis location of an edge of the calibration bar. The position identifiers, such as look-up tables in a microprocessor or computer that provide the X-Y coordinates of each of the vial receptacles in the racks, are modified to accommodate any slight skewing of the respective rack.
Another aspect of the invention is an improved stabilizing mechanism for the vials which are held by the gripper head and then lifted and moved. Gripper fingers are used for grasping the neck and cap of the vial, and a stabilizing ring surrounds the main part of the vial as the gripper head lifts the vial. The stabilizing or guide ring retracts as the gripper head moves to engage a vial in a rack when the vial is to be moved, to permit gripping the vial and then the ring extends under spring load to surround the vial so that cocking or other misalignment of the vial relative to the gripper head axis will be reduced or eliminated so that the vial will be properly orientated for placing into a vial holder station on the base, for example, a sampling station.
A series of sequentially controlled valves, coupled with a syringe type pump provides for the analysis of samples removed from the vials placed in the sampling station.
A vial handling device in the sampling station moves a vial having a specimen therein from a loading site where it is placed by the gripper head, to a sampling site, and includes a carrier adapted to hold the vial, an elevator coupled to the carrier, and a mechanism to translate the carrier laterally as the vial is transported from the loading site to the sampling site.
In another aspect of the invention, an autosampler device includes a base unit having a port therein, a central control circuit including a removable circuit module disposed proximate the port, and a panel which is sized and movably held to the base unit to alternately cover and expose the port, thereby providing access to the removable circuit module through the port.